In this paper, a compact and simple microstrip-fed slot antenna is proposed for ultra-wideband (UWB) applications, which consists of a circular patch and an open T-slot to realize the microstrip-line to slot transition well over a widened frequency range. The simulations and measurements show that this simple structure with the novel design generates a broadband impedance bandwidth of 10dB return loss from 2.5 to 12.5 GHz (BW=133.3%) adjustable by variation of its parameters. Details of the antenna design and experimental results of the constructed prototype are presented. In addition, a geometric parameters study of the proposed antenna is able to provide more useful information for antenna design.
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